I was mulling the p-zombie problem. For example, can we really have a world with only zombies which cannot be distinguished from sentient people? Although this might lead to the awkward situation that these zombies (in keeping up with real people) would discuss qualia related issues (like the color inversion problem) and the hard problem in general, although they would be lost as to as to why they discuss them. There would seem to be an internal contradiction which they themselves would make out (and presumably let us real humans know).
But seriously, there has to be a reason why evolution favored qualia. I have a feeling that feeling qualia makes a material difference to the behavior (and therefore survival) of an organism. And it leads to the postulate that there are behavior patterns that result because of qualia being perceived, and which would not occur given just pure functionalism. Note that the survival fitness of any life form depends not on the qualia perceived per se, but what it decides to do with it. Whatever be the decisions taken because of qualia being perceived, it needs to be translated back to physical behaviour. So there are broadly two pathways, sensory and motor, which are quite analogous to the real life case of the nervous system.
If a low form of life has purely reflexive instincts, qualia may not matter much. For example, an insect is not expected to be engaged in any high level thought. If it flies near a candle flame, maybe the heat can activate a reflexive behavior that causes the insect to beat its wings in a different manner instantly that causes it to avoid the flame. The insect need not even "feel" pain. We ourselves are capable of reflex action in avoiding a hot object or sharp knife, and only the spinal cord is involved in such cases. We do not make a conscious decision to withdraw from the harmful stimulus. It is possible that this reflex action behavior present in higher animals is just the original mechanism of our ancestors with a more rudimentary nervous system.
But lets take the example of a human engaged in some high level activity like reading a book. While reflexive behavior might help in avoiding certain kind of stimuli (like a bee sting), for some other stimuli which are nevertheless harmful, although over a longer time scale, there needs to be some sort of a "distraction mechanism" to tell the person that this is of higher priority and needs immediate attention. The qualia of pain seems to fit the candidature very well here. Thus someone could still carry out normal activities with a mild headache, but as it grows in intensity, he would ignore other activities and call the hospital. In fact, when the pain becomes intense, it completely hijacks the command center of the brain, and facilitates summoning of medical help. This obviously has survival value, since the pain might signal an impending stroke. If it were not pain, in what other manner could the person be alerted to the impending medical emergency? Since the action to be taken here is calling up the emergency room (which is a very complicated process compared to withdrawing a finger from a hot object), reflexive behavior is inadequate and the person's consciousness needs to get involved here. If we assume that the person has only one consciousness, then the person has to first consciously perceive the medical condition.
So whats the manner by which a person's conscious self is alerted to an emergency condition? We have ruled out reflexive behavior. The gateways to a conscious mind are qualia of some form. It is possible that instead of pain, one other alternative is that the person suddenly "knows" that there is something wrong, and also realizes the seriousness of it without perceiving pain. Then it would result in the same action, namely calling up the hospital. In fact, in ischemic strokes, instead of pain, there might be a mental qualia (transient loss of consciousness or suddenly forgetting where one is) which signifies the same. But unless one knows beforehand that these can be the warning signs of a stroke, the person may not give it the same degree of priority and delay in getting help for himself, with disastrous consequences. On the other hand, a person with a severe headache does not need to know that this could be the warning sign of a stroke. He might summon help just to get rid of the headache since it has become unbearable. Thus pain in itself will "lead" the person to the right course of action without the person actually having to know what it is about. Another example is being barefoot on a hot surface on a sunny day. If he were to stand there for a long time, his soles would likely get burnt. But when the pain grows, the person would start moving to the shade, not because he consciously realizes that standing there any longer would damage his feet, but to mitigate the signal of pain itself.
Therefore, when some stimuli (internal or external) needs attention and a complex response that can be mediated only by conscious behavior, qualia are the gateways through which those stimuli can bring themselves to the attention of the conscious mind. So once an organism develops consciousness (for whatever reason), evolution would favor all important stimuli for which complex mind-mediated action to be needed to manifest themselves as appropriate qualia that leads to the correct behavior from an evolutionary standpoint. This would be a runaway situation once consciousness develops in a system.
I have only detailed why qualia might be helpful in conscious beings. I have not really hinted at why zombies are at a disadvantage compared to sentient beings. After all, by definition, zombies have the same behavior as the latter and should not be discriminated against in evolution.
In a subsequent blog I will discuss why zombies may not even be possible. In other words, beings that follow strict physicalism will be at a disadvantage compared to beings that have consciousness and qualia. And zombies (which by definition strictly follow physicalism) will lose out to conscious beings.